There has recently been a pronounced increase in the types of communication applications that require the use of wireless data transfer. Such applications include, for example, video conferencing, video-on-demand, high speed Internet access, high speed local area networks, online gaming, and high definition television. In the home or office, for example, computing devices continue to be connected using wireless networking systems. Many additional types of devices are also being designed with wireless communication in mind.
At frequencies below about 3 GHz, signals tend to be less directional, thereby causing them to impact and reflect off of nearby objects. These reflected signals result in what is known as “multipath,” which involves the reflected signal arriving at the intended receiver later than the original signal. One way to minimize this effect has been to parcel the frequency spectrum by licensing a given spectrum band to a single signal provider in a given area.
At higher frequencies (e.g. from about 3 to about 60 GHz), signals become somewhat directional, which largely reduces the multipath issue mentioned above. As such, the number of signal providers that can coexist in a given space and/or frequency increases dramatically. The 57-64 GHz (“60 GHz band”) band is located in the millimeter-wave portion of the electromagnetic spectrum and has been largely unexploited for commercial wireless applications. This spectrum is unlicensed by the FCC in the United States and by other bodies world-wide. In addition to the higher-data rates that can be accomplished in this spectrum, energy propagation in the 60 GHz band has unique characteristics that make possible many other benefits such as excellent immunity to interference, high security, and frequency re-use.
Transmissions at 60 GHz can be much more directional in nature, and can co-exist with other signal sources placed in very close proximity to each other. Directivity is a measure of how well an antenna focuses its energy in an intended direction. Highly focused antennas minimize the possibility of interference between links in the same geographic area, minimize the risk that the transmission will be intercepted, and maximize performance by only expending energy in the intended direction.
Low power transmissions (i.e. lower than the FCC allowed 40 dBm) in the 60 GHz range are limited in range in both free air, attributable to oxygen absorption of the energy, and is easily stopped or reflected by structures such as walls. These seeming limitations contribute to the inherent security of the transmissions.
Omni-directional transmissions are useful in point to multi-point transmissions, but are energy wasteful in the case of point to point transmissions. Focused, or directional, transmitters of the same power as an omni-directional transmission will far exceed the range of the omni-transmitter OR if the same range is desired, then the focused transmitter will use significantly less power. The focused transmitters enable like-frequency focused transmitters to co-exist in closer proximity than omni-directional transmitters. By placing multiple directional transmitters in parallel the data rate capability is multiplied by the number of transmitters. Data rates are directly related to available bandwidth and signal-to-noise (SNR) in the bandwidth. The available SNR & bandwidth dictate modulation schemes, which in turn affects bits per symbol. For example, 1 GHz of bandwidth using a simple, robust DQPSK modulation scheme (2 bits per symbol) yields 2 Giga bits per second (Gbps). To achieve more bits per symbol requires a quieter data channel as well as more sophisticated modulators and demodulators. In the case of 60 GHz where data rates easily exceed 2 Gbps this results in extraordinarily high data rates across relatively short ranges.
One method to focus or direct the transmission is to use a “horn” antenna, but these are expensive, large, and fixed in terms of direction and focus. There is still a need for more directed transmissions than what is possible with typical 60 GHz transmissions, and for higher-data rate transmissions. Thus, there exists a need for a system and method for high frequency parallel RF transmissions that overcomes the aforementioned problem, while still maintaining the benefits of 60 GHz transmissions.